The fuel consumption of an idling stop vehicle can be improved in such a manner that an engine is turned off while the vehicle stops. However, since a lead-acid battery supplies power to all of an air conditioner, a fan, etc. during idling stop, the lead-acid battery is likely to be in an insufficiently-charged state. In order to overcome the insufficiently-charged state, a high charge acceptance is required for the lead-acid battery so that the lead-acid battery can be more charged for a short period of time. Moreover, since the idling stop vehicle frequently repeats ON/OFF of the engine, succeeding discharging is performed before lead dioxide and lead are, by charging. recovered from lead sulfate generated by preceding discharging. Thus, the life of the lead-acid battery is likely to decrease. For such reasons, a high durability is also required for the lead-acid battery in order to overcome a decrease in life.
In order to improve the charge acceptance of the lead-acid battery, Patent Document 1 describes a lead-acid battery including an electrolyte containing aluminum ions. The aluminum ions exhibit the effect of reducing, in discharging, coarsening of lead sulfate generated at positive and negative electrodes, thereby improving the charge acceptance of the lead-acid battery.
Patent Document 1 also describes that a lead-antimony based alloy layer formed on a surface of a negative electrode grid can reduce a decrease in thickness of an ear part of the negative electrode in an idling stop mode.
In order to improve the durability of the lead-acid battery, Patent Document 2 describes a lead-acid battery in which a lead alloy layer containing antimony is formed on a surface of a negative electrode grid containing no antimony. The lead alloy layer containing antimony exhibits the effect of efficiently performing charge recovery of a negative electrode plate, thereby improving the durability of the lead-acid battery.
Patent Document 3 describes a lead-acid battery in which a negative electrode grid containing no antimony is filled with a negative electrode active material containing antimony and the mass ratio of the negative electrode active material to a positive electrode active material falls within a range of 0.7 to 1.3. The antimony added to the negative electrode active material exhibits the effect of decreasing a hydrogen overvoltage of a negative electrode, thereby improving the charge acceptance of the negative electrode active material. Moreover, since the mass ratio of the negative electrode active material to the positive electrode active material falls within a range of 0.7 to 1.3, elution of the antimony from the negative electrode active material to the electrolyte in over-discharging of the lead-acid battery and deposition of the antimony on an ear part of the negative electrode can be reduced. This can reduce corrosion of the ear part of the negative electrode.
Patent Document 4 discloses that, in order to overcome a short life caused by an increase in frequency of discharging due to the use conditions where the frequency of temporary stop accompanied by idling stop is high, the density of a positive electrode active material is 3.5 to 4.5 g/cc, the specific gravity of an electrolyte is 1.240 to 1.260 (20° C.), and the amount of carbon which is an additive of a negative electrode plate is 0.5 to 2.0% per mass of a negative electrode active material.
Patent Document 5 describes a control valve type lead-acid battery in which the mass ratio of sulfuric acid in an electrolyte to a positive electrode active material falls within a predetermined range and sodium tetraborate is added to the electrolyte. This reduces deposition of dendrites of lead by re-charging after over-discharging, thereby reducing or preventing internal short-circuit.
Patent Document 6 describes the technique of reducing lead ion generation accompanied by a decrease in sulfuric acid concentration in over-discharging by adding alkali metal sulfate such as Na2SO4 to an electrolyte and reducing or preventing occurrence of short-circuit between positive and negative electrodes by growing PbSO4 on the negative electrode in charging. The Na2SO4 added to the electrolyte exhibits the effect of reducing a decrease in conductivity of the electrolyte due to a decrease in sulfuric acid concentration in over-discharging and improving charge recovery after over-discharging.